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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

How reliable are climate models?

What the science says...

While there are uncertainties with climate models, they successfully reproduce the past and have made predictions that have been subsequently confirmed by observations.

Climate Myth...

Models are unreliable
"[Models] are full of fudge factors that are fitted to the existing climate, so the models more or less agree with the observed data. But there is no reason to believe that the same fudge factors would give the right behaviour in a world with different chemistry, for example in a world with increased CO2 in the atmosphere." (Freeman Dyson)

There are two major questions in climate modeling - can they accurately reproduce the past (hindcasting) and can they successfully predict the future? To answer the first question, here is a summary of the IPCC model results of surface temperature from the 1800s - both with and without man-made forcings. All the models are unable to predict recent warming without taking rising CO2 levels into account. Nobody has created a general circulation model that can explain climate's behavior over the past century without CO2 warming.

Predicting/projecting the future

A common argument heard is "scientists can't even predict the weather next week - how can they predict the climate years from now". This betrays a misunderstanding of the difference between weather, which is chaotic and unpredictable, and climate which is weather averaged out over time. While you can't predict with certainty whether a coin will land heads or tails, you can predict the statistical results of a large number of coin tosses. In weather terms, you can't predict the exact route a storm will take but the average temperature and precipitation over the whole region is the same regardless of the route.

There are various difficulties in predicting future climate. The behaviour of the sun is difficult to predict. Short-term disturbances like El Niño or volcanic eruptions are difficult to model. Nevertheless, the major forcings that drive climate are well understood.

A paper led by James Risbey (2014) in Nature Climate Change takes a clever approach to evaluating how accurate climate model temperature predictions have been while getting around the noise caused by natural cycles. The authors used a large set of simulations from 18 different climate models (from CMIP5). They looked at each 15-year period since the 1950s, and compared how accurately each model simulation had represented El Niño and La Niña conditions during those 15 years, using the trends in what's known as the Niño3.4 index.

Each individual climate model run has a random representation of these natural ocean cycles, so for every 15-year period, some of those simulations will have accurately represented the actual El Niño conditions just by chance. The study authors compared the simulations that were correctly synchronized with the ocean cycles (blue data in the left frame below) and the most out-of-sync (grey data in the right frame) to the observed global surface temperature changes (red) for each 15-year period.

Figure 2: Red: 15-year observed trends for each period. Blue: 15-year average trends from CMIP5 runs where the model Niño3.4 trend is close to observations. Grey: average 15-year trends for only the models with the worst correspondence to the Niño3.4 trend. The sizes of the dots are proportional to the number of models selected. From Nature Climate Change

The authors conclude,

When the phase of natural variability is taken into account, the model 15-year warming trends in CMIP5 projections well estimate the observed trends for all 15-year periods over the past half-century.

It's also clear from the grey figure that models that are out-of-sync with the observed changes in these ocean cycles simulate dramatically higher warming trends over the past 30 years. In other words, the model simulations that happened not to accurately represent these ocean cycles were the ones that over-predicted global surface warming.

Climate models have also been accurately projecting global surface temperature changes for over 40 years. Climate contrarians have not:

Figure 3: Various global temperature projections by mainstream climate scientists and models, and by climate contrarians, compared to observations by NASAGISS. Created by Dana Nuccitelli.

Uncertainties in future projections

A common misconception is that climate models are biased towards exaggerating the effects from CO2. It bears mentioning that uncertainty can go either way. In fact, in a climate system with net positive feedback, uncertainty is skewed more towards a stronger climate response (Roe 2007). For this reason, many of the IPCC predictions have subsequently been shown to underestimate the climate response. Satellite and tide-gauge measurements show that sea level rise is accelerating faster than IPCC predictions. The average rate of rise for 1993-2008 as measured from satellite is 3.4 millimetres per year while the IPCC Third Assessment Report (TAR) projected a best estimate of 1.9 millimetres per year for the same period. Observations are tracking along the upper range of IPCC sea level projections.

Similarly, summertime melting of Arctic sea-ice has accelerated far beyond the expectations of climate models. The area of sea-ice melt during 2007-2009 was about 40% greater than the average prediction from IPCC AR4 climate models. The thickness of Arctic sea ice has also been on a steady decline over the last several decades.

Figure 5: Comparison of observed September minimum Arctic sea ice extent through 2008 (red line) with IPCC AR4 model projections. The solid black line shows the mean of the 13 models, and dashed black lines show the range of the model results. The 2009 minimum was calculated at 5.10 million km2, the third lowest year on record and still well below the IPCC worst case scenario. (Source: Copenhagen Diagnosis, 2009)

There's one chart often used to argue to the contrary, but it's got some serious problems, and ignores most of the data.

Do we know enough to act?

Skeptics argue that we should wait till climate models are completely certain before we act on reducing CO2 emissions. If we waited for 100% certainty, we would never act. Models are in a constant state of development to include more processes, rely on fewer approximations and increase their resolution as computer power develops. The complex and non-linear nature of climate means there will always be a process of refinement and improvement. The main point is we now know enough to act. Models have evolved to the point where they successfully predict long-term trends and are now developing the ability to predict more chaotic, short-term changes. Multiple lines of evidence, both modeled and empirical, tell us global temperatures will change 3°C with a doubling of CO2 (Knutti & Hegerl 2008).

Models don't need to be exact in every respect to give us an accurate overall trend and its major effects - and we have that now. If you knew there were a 90% chance you'd be in a car crash, you wouldn't get in the car (or at the very least, you'd wear a seatbelt). The IPCC concludes, with a greater than 90% probability, that humans are causing global warming. To wait for 100% certainty before acting is recklessly irresponsible.

Comments

Look at plate 1 in Hansen's 88 paper, the model includes the oceans. Hansen's Scenario C is the one that most closely matches the "Land – Ocean" temperature.

John Cook wrote:
"A way to test the accuracy of models is through hindcasting - see whether they successfully predict what has been observed over the past century."

Not true for any model. All that shows is they can fit the model to the history. That is beside the point as the IPCC does not claim that the models can predict anything.

John Cook wrote:
"The key point is that all the models fail to predict recent warming without taking rising CO2 levels into account."

Given enough "tunable parameters" that should come as no surprise. The modelers also assume that there is some positive feedback, there is no proof that this is the case. Here is one for you straight from the IPCC, Chapter 8, page 596:

"The number of degrees of freedom in the tuneable parameters is less than the number of degrees of freedom in the observational constraints used in model evaluation."

IOW, the models are nothing more then sophisticated curve fits.

Calling the models "predictions" does not instill confidence that you have done your homework.

Kevin E. Trenberth
http://blogs.nature.com/climatefeedback/2007/06/predictions_of_climate.html
"In fact there are no predictions by IPCC at all. And there never have been. The IPCC instead proffers “what if” projections of future climate that correspond to certain emissions scenarios."

And from the same letter:
"Even if there were, the projections are based on model results that provide differences of the future climate relative to that today. None of the models used by IPCC are initialized to the observed state and none of the climate states in the models correspond even remotely to the current observed climate. In particular, the state of the oceans, sea ice, and soil moisture has no relationship to the observed state at any recent time in any of the IPCC models."

John Cook wrote:
"Satellite measurements show that the troposphere is warming"

The models predict that the troposphere should warm faster then the surface, it isn't.

Response: Re tropospheric warming, I recommend reading Satellite show little to no warming in the troposphere. The argument over "prediction" vs "projection" is semantics. Kevin Trenberth is merely saying we don't know with certainty what future emissions will be so we make predictions based on various emission scenarios. However, lest it be a stumbling block, I'll update the text. Thanks for the feedback!

Models are the biggest gun in the arsenal for AGW. What people like Dyson are telling us is that the models use assumptions that are not validated by observation and that cannot account for many known effects. The models might be right but they haven't got a good track record except in hind sight. (After they've been fudged to fit the past) Someday they will probably be good they are better than 20 years ago.

Leaving aside the silly notion that you can 'prove' a model's accuracy by checking it's fitting to the historical record--I mean honestly, you are aware that these models are tweaked *until* they fit the historical record, aren't you? The past is not the problem.

The Hansen forecast sounded impressive, so I looked over the paper and did some googling. There is definitely a different spin on the accuracy of the forecast. Discussed here:

http://www.climateaudit.org/?p=796

which demonstrates that scenario B is nowhere near the perfect fit implied by your article or Hansen. Hansen could be right, but he doesn't seem to explain where he is getting his data from. I can only find vague references to 'Station Data' and 'Land-Ocean'. What data is it he is using? How has it been adjusted? At least the sceptical article above is up front on where the data is coming from. This doesn't prove that Hansen is wrong. But it doesn't leave one with a high degree of confidence either.

Well, here is NASA telling us there is no meaningful comparison of models to observed global temp change
"The analysis by Hansen et al. (2005), as well as other
recent studies (see, e.g., the reviews by Ramaswamy
et al. 2001; Kopp et al. 2005b; Lean et al. 2005; Loeb
and Manalo-Smith 2005; Lohmann and Feichter
2005; Pilewskie et al. 2005; Bates et al. 2006; Penner
et al. 2006), indicates that the current uncertainties
in the TSI and aerosol forcings are so large that they
preclude meaningful climate model evaluation by
comparison with observed global temperature change.
These uncertainties must be reduced significantly for
uncertainty in climate sensitivity to be adequately con-
strained (Schwartz 2004). Helping to address this chal-
lenging objective is the main purpose of the National
Aeronautics and Space Administration (NASA) Glory
mission, a remote sensing Earth-orbiting observatory"

"The strong emphasis placed on the realism of the simulated base state provided a rationale for introducing ‘flux adjustments’ or ‘flux corrections’ (Manabe and Stouffer, 1988; Sausen et al., 1988) in early simulations. These were essentially empirical corrections that could not be justified on physical principles, and that consisted of arbitrary additions of surface fluxes of heat and salinity in order to prevent the drift of the simulated climate away from a realistic state. The National Center for Atmospheric Research model may have been the first to realise non-flux-corrected coupled simulations systematically, and it was able to achieve simulations of climate change into the 21st century, in spite of a persistent drift that still affected many of its early simulations. Both the FAR and the SAR pointed out the apparent need for flux adjustments as a problematic feature of climate modelling (Cubasch et al., 1990; Gates et al., 1996).

By the time of the TAR, however, the situation had evolved, and about half the coupled GCMs assessed in the TAR did not employ flux adjustments. That report noted that ‘some non-flux adjusted models are now able to maintain stable climatologies of comparable quality to flux-adjusted models’ (McAvaney et al., 2001). Since that time, evolution away from flux correction (or flux adjustment) has continued at some modelling centres, although a number of state-of-the-art models continue to rely on it."

A 'flux adjustment' is where you discover that the model's predictions start to vary so much from the historical record that you have to go in and change the values inside the software to re-fit the model to what's actually happening. Very confidence inspiring. And what does 'a number of' mean? 50%? 20%? 80%? How many of these models are manually fiddled with to get them to continue to work...?

Here is another posting assessing Hansen's model work in a not very favourable way:

Whether these alternate assessments of Hansen's work stand up is a separate issue. I would point out we should not accept them blindly any more than we should blindly accept Hansen's paper on how brilliant Hansen's previous work was, as this naive article does...

"The models might be right but they haven't got a good track record except in hind sight. (After they've been fudged to fit the past)"

"Leaving aside the silly notion that you can 'prove' a model's accuracy by checking it's fitting to the historical record--I mean honestly, you are aware that these models are tweaked *until* they fit the historical record, aren't you?"

Nonsense. Are you saying that Hansen, way back in 1988, was able to travel in a time machine to 2006 and back, so that he could make the adjustments to his 1988 models to make them agree all the way to the present?

No, we are saying that Hanson's model from 1988 does not fit the present, even his conservative projections are significantly high of actual observation at this point. (High relative to the ground based measurements and wildly high compared to satellite and balloon measurements to be more specific)

If a model can't take past conditions and produce results that fit current reality it would be obviously useless.

However since modelers are not simpletons that isn't the problem that was being discussed! The problem is just because current models have been changed so they can somewhat be used to fit past observations that doesn't mean those changes were the correct changes, therefore it doesn't mean that they are making correct predictions. The models still contain assumptions for various parameters that have not or perhaps can not presently be varified.

Freeman Dyson is correct here, Models are improving but they have a long way to go before they are better than educated guesses.

You should read Dyson's entire statement this is a bit out of context.

Look at the temperature predictions in Hansen et al. (2006) and Hansen et al. (1998). They are _exactly_ _the_ _same_. The 1998 model has _not_ been changed at all, and it still agrees all the way to 2006. All your talk about "fudge factors" can't explain that.

It is taken from the US Senate Committee on the Environment and Public Works - http://epw.senate.gov/public/index.cfm?FuseAction=Minority.SenateReport#report

Physicist Dr. Freeman Dyson, Professor Emeritus of Physics at the Institute for Advanced Study, in Princeton, is a fellow of the American Physical Society, a member of the US National Academy of Sciences, and a fellow of the Royal Society of London. Dyson called himself a "heretic" on global warming.

"Concerning the climate models, I know enough of the details to be sure that they are unreliable. They are full of fudge factors that are fitted to the existing climate, so the models more or less agree with the observed data. But there is no reason to believe that the same fudge factors would give the right behavior in a world with different chemistry, for example in a world with increased CO2 in the atmosphere.," Dyson said in an April 10, 2007 interview. Dyson is also a fellow of the American Physical Society, a member of the US National Academy of Sciences, and a fellow of the Royal Society of London.

I'll also raise the question whether anyone really believes this extract (from above) which appears to be a basic premise for the page:

"This betrays a misunderstanding of the difference between weather, which is chaotic and unpredictable and climate which is weather averaged out over time. While you can't predict with certainty whether a coin will land heads or tails, you can predict the statistical results of a large number of coin tosses. Or expressing that in weather terms, you can't predict the exact route a storm will take but the average temperature and precipitation will result the same for the region over a period of time."

It's a false analogy. Random *independent" events provide statistical certainty over a period of time. The climate does not fit this description.

Can anyone provide some evidence -peer reviewed citations - that long range climate forecasting is more accurate than weather forecasting? I know the IPCC claimed it in their report but they didn't backup the claim.

Response: That's the problem with using analogies - the comparison always breaks down at some point when you compare it directly. The main point is the contrast between short term, random unpredictability and long term, statistical summations. While weather is chaotic and non-linear, long term climate trends are discernable and predictable. As is seen in these peer reviewed studies analysing the success of climate forecasts.

A common comment regarding GCMs is that they do not account for clouds very well. This is a substantial weakness. There have been assertions that warming increases atmospheric water vapor which, through a feedback mechanism, increases warming. Certainly increased atmospheric water vapor would produce more, lower-level clouds. How do the GCMs account for this? A simple cloudy-planet point model where standard atmosphere tables are used to get average cloud temperature vs altitude shows that a change of average cloud altitude of 305 meters would result in an eventual average earth temperature change of 0.75C. Many other factors known to influence cloud formation are not accounted for in the GCMs.

Frankbi said:
"And besides, if models can be "fudged" to fit anything -- as our `skeptics' claim -- why are the _same_ `skeptics' saying that they can't get Hansen's model to fit the data?

Can it be because our `skeptics' are simply full of junk?"

I am surprised that John did not reply to this, but I assume he does not have the time to respond to every nonsensical claim that appears on his board.

Frank, if you do not know that GCMs (and many other models) are "tweaked" to fit past data, then you have no place attacking others. It is common practice, and there is little that is nefarious about it, though it may appear as such. You probably know that there are many uncertainties and complexities in the climate system, and in attempting to model such a system, you must used what has already been observed to better your understanding and accuracy. If models were based purely upon theory for such a complex system, they would appear wildly inaccurate and worthy of no utilization.

The IPCC summary of computer simulations you link above only go back to 1850 and blurs out problems with individual models by replacing the spaghetti curve with a grayed out region. (Errors in the simulations are highly correlated from year to year, the figure makes it seem they are not, which is false and misleading.)

Also did you notice the huge 0.3°C anomaly around 1940-1950 that the models, even with the fuzzing provided by IPCC, are unable to explain?

Where did that warming come from? I would conclude from that, that we aren't at the place yet, even for a 150-year period with a lot of fudge factors thrown in, where we can accurately describe past climate, let alone accurately predict future climate.

Secondly did you notice that there was very little anthropogenic forcing before 1970, according to the models? Have you ever considered how disingenuous it is, given this fact, to compare glaciers from e.g. 100 years ago to current, when the models say that almost all warming prior to 1970 was natural?

Yes, I do know that model parameters are usually adjusted according to some past data, _and_ the resulting model has to be validated with data that are _not_ used to configure the models in the first place. If I didn't make this clear enough, my apologies.

From my understanding, this approach of tweaking and holdout validation is what climate scientists have been doing. And it's perfectly good science, of course.

Poptech
When I was in college we were taguht Fortan IV, even though it had already been supplanted by Fortan 77. I did not realize that anyone was still using it. My own last experience was in SAS and that was in the 90s. Are you saying that these climate models are being coded in Fortran?

Poptech, nice job of trying to help people understand what computer modeling is and what it can do.

Folks, if a climate model doesn't predict past data 100% perfectly then it's useless. You can create an infinite number of different mathematical models that will predict any data series 100% perfectly. To deserve any respect these climate models must predict the previous data perfectly as a start, none should even be thought about unless it does that, and then it has to predict the future better than a simple polynomial fit that also perfectly predicts past data.

Frankbi, all the facts in Poptech's post are verifiable. I learned them in school. His analysis is spot on.

http://www.realclimate.org/index.php/archives/2008/05/what-the-ipcc-models-really-say/#comment-87205
on the Skeptic article, by the other author on the same issue.

Koutsoyiannis mentioned here:

"Cohn and Koutsoyiannis, one of them the author of the very paper that I had criticized, sat down next to me. We nevertheless had a very civilized and friendly chat, deciding to disagree on the matter of natural trends.

But Dr. Koutsoyiannis commended us for being respectful in our reply to his comments. I think this is a very important issue – we have to be respectful, sincere, and show courtesy in our criticism, even when we argue why we think that a paper has flaws. ..."
http://www.realclimate.org/index.php/archives/2008/04/egu-2008/

Use the Search box at the top of the RC page, paste in:
Koutsoyiannis
Dr. Koutsoyiannis posts there in two of the discussions.

I didn't think Koutsoyiannis was writing up a "skeptic article", but rather an assessment of climate models.

"'Cohn and Koutsoyiannis, one of them the author of the very paper that I had criticized, sat down next to me. We nevertheless had a very civilized and friendly chat, deciding to disagree on the matter of natural trends.

But Dr. Koutsoyiannis commended us for being respectful in our reply to his comments. I think this is a very important issue – we have to be respectful, sincere, and show courtesy in our criticism, even when we argue why we think that a paper has flaws. ...'"

I don't see how this is relevant-- the paper that Rasmus criticized was a paper titled "Nature's style: Naturally trendy" by Timothy Cohn and
Harry Lins. The "But Dr. Koutsoyiannis commended us for being respectful in our reply to his comments" part of it involved comments made by Koutsoyiannis on a 2006 realclimate thread.

So hank, I am not exactly sure where you are getting at with your comment here. Just a little background information on Koutsoyiannis?

It studies the accuracy of climate models. Basically compares the model's predictions vs what happened. The conclusion was that climate models don't predict forward very well. I don't have the background to judge whether this article is credible but it did go through a peer reveiw process.

Oh - and in my research on this subject I found the chart you had above 'Average Mean Global Temperature Change' had been updated over on ClimateAudit:

http://www.climateaudit.org/?p=3354#more-3354

Can I trust the updated charts posted there? They seem to show actual temperature date significantly diverging from Hansen C (ie: lower). Again - I'm not the expert so I'm here asking questions of those who are :-). Thanks.

To put the Global Warming issue in context, consider:
1. That average global temperature has decreased since 1998. The anomalies from NOAA data are:
1998 0.5763
1999 0.3947
2000 0.3629
2001 0.4934
2002 0.5573
2003 0.5565
2004 0.5336
2005 0.6044
2006 0.5428
2007 0.5458
Jan to June 2008 average 0.44
2. That GCMs (Global Climate Models) do not yet adequately account for the absorbed infrared radiation energy that is transported up by atmospheric convection currents.
3. That GCMs are not yet capable of dealing objectively with clouds so they are accounted for with subjective parameterization.
4. That currently used GCMs invoke water vapor positive feedback that climate history shows to be not valid.
5. That the GCM users/creators won’t divulge to competent evaluators some of the details of their computer programs.
6. That the only indicators that human activity causes global warming are these GCMs.
7. That the multi-billion dollar government grants for ‘climate research’ depend on ominous prediction of looming catastrophe.
8. That over 30,000 qualified scientists and engineers have signed a document stating that human activity has had no significant influence on climate.

1. probability and possibility are two different things.
You may show statistically that something is probable and therefore, sooner or later will happen. This is only true mathematically and not necessarily works in the real world. Any computer model that includes assumptions, 'tweaked' data, or excludes any factors relevent to the model will give a rubbish result.

2. Remember the Chaos Effect. Small things through iterative action can have BIG consequencies, so the apparently small and irrelevent must be accounted for.
Worse yet, we don't even know if we know ALL the factors influencing the climate....so any model will be suspect.

Poptech
Re: comment 29
Please correct me if I am wrong but was not Fortran 66 (1966) not machine dependent as well as structure dependent? I am not familiar with Fortran 95 as I stopped using Fortran 77 around 1983 and switched to Pascal so my code would be transportable.

Just read an interesting abstract on the effect of the moon on the monthly GMT.
"Over the past fifty years, the Diurnal Temp Range has decreased by about half a degree.Conventional wisdom blames this on the greenhouse effect. But this decrease is just a trend observed in data that vary over shorter
timescales. Cerveny and Balling show that for the period between 1950 and 1995, the DTR fluctuates with the phases of the Moon. It tends to increase towards Full Moon, and tends to be lowest at New Moon. Simple
monthly differences in DTR between New Moon and Full Moon may be as much as 0.309 ºC -- in other words, 60% of the entire 50-year decrease. The message should be clear: all possible sources of variation should be
investigated before blaming human activity alone for observed changes in climatic parameters."

There is a correlation between full moon and monthly DTR variations most of which is ascribed to the changing earth/moon barycentre. This has prompted a look at the effects of a shifting sun/earth/moon barycentre on earth climate.
Another piece in the puzzle?

I would imagine that the difference between full and new is reflected sunlight and whatever radiation it may contain. This would have an effect on GHGs (I am thinking water vapor and methane which a recent article at LiveScience talks about.

Re: "This has prompted a look at the effects of a shifting sun/earth/moon barycentre on earth climate."

QM: Yes, just recently, which prompted me to look for further info on how a shifting barycentre could affect climate.
One thought which I am currently pursuing is adiabatic cooling of the upper atmoshere caused by the tidal effect of sun/moon. As the barycentre moves it causes the shape of the atmospheric envelope to alter, effectively expanding the volume, which should cause a cooling effect.

Sandy Winder:
Gustav was weather, not climate. Gustav was the end product of the climate process.
Weather can be predicted over VERY short periods with a reasonable level of accuracy; at present, climate cannot. This is a good chunk of what the argument is all about. The uncertainty with Gustav was not that it would hit, but exactly where and at what level ( eventually I think downgraded to Cat2) so it would have been foolish to ignore it.
A side benefit of the dispute is that we are learning a lot more about climate,history,the biosphere etc.

QM:
The earth-moon barycentre is around 1700km BENEATH our crust..so the tidal effect of the moon/sun would 'stir up' the lower mantle...presumably a very low frequency effect....and increase surface volcanic activity??

Apparently climatologists do not have much grounding in how feedback works. Unaware of their ignorance, they invoke net positive feedback in their GCMs. This mistake causes the GCMs to predict significant ‘enhanced global warming’. Anyone who has the ability and interest to look at the NOAA data from Vostok Ice Cores for the last glaciation (and prior glaciations) will discover that, repeatedly, a temperature increasing trend changed to a decreasing trend with the carbon dioxide level higher than it had been when the temperature was increasing. Graphs of NOAA and other credible data, all fully sourced so they can be verified, can be seen at http://www.middlebury.net/op-ed/pangburn.html. (The web site is controlled by Middlebury, not me.) Those who understand how feedback works will know that this temperature trend reversal is not possible with significant net positive feedback. Thus, as far as global climate is concerned and contrary to the assumption in the GCMs, significant net positive feedback does not exist. Other assessments from entirely different perspectives also determine that there is no significant net positive feedback. They can be seen at http://www.climate-skeptic.com/2008/01/index.html and http://www.weatherquestions.com/Roy-Spencer-on-global-warming.htm

"In addition phytoplankton emit Dimethyl Sulphide (DMS), which reacts with oxygen in the atmosphere to produce sulphur dioxide. This acidic gas forms tiny droplets which help to seed clouds over the ocean, and these reflect sunlight thus cooling the planet. Measurements of methane sulphonic acid (MSA, which is derived from DMS) in ice core bubbles indicate that there were more phytoplankton in the polar oceans during the ice ages, as expected from the theory above. Therefore as the climate gets warmer there will be less seeding of clouds over the ocean - clearly a positive feedback."

Atmospheric water vapor is also clearly a positive feedback. There are also negative feedbacks. Dr. Richard Lindzen has identified one, his iris effect. Response of the climate system depends on the combined effect of all feedbacks, known or not. When all are combined, the NET feedback can not be significantly positive. This is mandated by the temperature trend reversals of the last and previous glaciations.

Dan:
Depends what you take as significant. The time span is important,as well as the net feedback quantity.
A very small change over a very long period ( like glacial periods) can eventually have a profound effect, This is the basis of Chaos Theory.
One of our major problems is that we do not have enough hard data to quantify these matters to sufficient degree to allow a reasonable model to be constructed.
We have a lot of information, knowledge and some data, but mostly we have guesstimates derived by various means ( some quite dubious), and that isn't good enough for a system of this complexity.

There is only one complete and exact computer of global climate and that is the planet itself. By definition it complies with all laws of nature including physics and quantum mechanics. Einstein said “no number of tests can prove I’m right but only one is needed to prove I’m wrong”. That one test that proves to be wrong the theory that added atmospheric carbon dioxide causes global warming was run on the planet computer and the results are archived in the Vostok ice cores. They show that, repeatedly, a temperature increasing trend changed to a decreasing trend with the carbon dioxide level higher than it had been when the temperature was increasing. Those who understand how feedback works will know that this temperature trend reversal is not possible with significant net positive feedback. Thus, as far as global climate is concerned and contrary to the assumption in the GCMs, significant net positive feedback does not exist.

Dan, you certainly do talk a lot of nonsense, and you seem to have gone to extraordinary lengths on your webpage to put together a deliciously incorrect view of the science!

Let's look at just a couple of things:

(1) ["The planet plunged in to the Andean-Saharan ice age 440 million years ago10 when the carbon dioxide level was over ten times higher than now."]

No.....there certainly does seem to have been significant glaciation dated to around 445.6 mya - 443.7 mya, but the atmospheric CO2 levels for this period are simply not known. You seem to have fallen for the trick of some dubious character who has drawn straight lines across vast ranges (10’s to 100's of millions of years) of geological time based on some unspecified temperature estimates (your posts on this thread are displaying that odd habit of denigrating pukka science by misrepresentation while at the same time embracing stuff that is very obviously ludicrous rubbish!).

I would expect everyone can understand the problem that if there are one or two paleo proxies (temp or CO2, for example) known for some periods in the past, that one can only say that that's what the temperatures/CO2 levels were AT THOSE PARTICULAR TIMES. One can't draw a line between the points and consider that the temperature/CO2 levels over vast intervening periods is thus established. Imagine an equally dumb geologist from the far future dating atmospheric CO2 level estimates from 430,000 years ago and 1000 years ago. "Goodness", he might say, extrapolating massively between limited data points in gay Scotese style, "highish CO2 levels right through this period. And yet there is evidence for multiple ice cap incursions right down to the South of England and deep into North America. Clearly there can't be any relationship between atmospheric CO2 and temperature"

Doh!

You need to go back and look at the relevant science, rather than trawling for dodgy “information” on websites[***]! The science has been compiled, for example, in a recent review by Royer:

Sadly there isn't a proxy CO2 measure for the late Ordovician glacial period. So we don't know if there is a mismatch between atmospheric CO2 levels and evidence for a cold spell then. It's rather clear (see Royer review, for example, and the masses of cited data therein, or the other articles cited just above) that where paleoproxies for atmospheric greenhouse gas levels and cold/warm spells are dated contemporaneously, that there is a rather good match (high CO2 associated with warm periods/low atmospheric CO2 with cold periods).

(ii) Surely by now everyone can understand the rather simple contributions to ice age cycles and the fundamental differences between solar driven effects (with CO2/water vapour/albedo feedbacks) and greenhouse gas driven effects of the sort that we are now seeing. I find it hard to believe that you consider that you’ve found something worth making such a fuss over, as if there’s something about the lag between temperature and CO2 levels in the Vostock core that is not obvious, rather well-understood and pretty consistent with what we know about greenhouse gases and their effects.

Let’s look at what happens during the ice age cycles driven by the small, painfully slow variations in the Earth’s orbital properties (Milankovitch cycles). As the pattern of insolation changes through these cycles the Earth warms (in a glacial to interglacial transition), ice sheets recede, albedo effects amplify the warming, the warming oceans release CO2 into the atmosphere resulting in further warming, atmospheric water vapour levels rise, and so on. Obviously, since the primary inducer of the warming is increased solar radiation, and the atmospheric CO2 rise is a result largely of the release of CO2 from the oceans, the temperature rises in advance of the atmospheric CO2 levels. That’s pretty obvious and uncontroversial (part of the lag is apparently also due to interhemispherical effects).

Going the other way (your example of events 112,000 years ago), it’s not surprising that decreased polar insolation resulted in cooling in advance of the lowering of atmospheric CO2 levels. It takes rather a long time for atmospheric CO2 to be absorbed from the atmosphere, and there’s nothing surprising about the fact that as one “lowers the heater” that the Earth cools while CO2 levels remain relatively high, as CO2 is very slowly reabsorbed by the oceans and terrestrial environment..

And of course the CO2 level changes are small and the rates of change are tiny compared to present day, where the warming we are seeing is the result of enhanced greenhouse effects with a relatively constant solar insolation. So whereas during the last glacial to interglacial period, for example, atmospheric CO2 rose by around 80 ppm over 5000 years (1.6 ppm per 100 years averaged over the transition), now atmospheric CO2 levels are rising at well over 100 times faster (2-2.5 ppm per year).

Everyone that takes the smallest effort to inform themselves is aware of the essential differences between ice age transitions (Milankovitch cycles drive extremely slow variations in atmospheric CO2 with very slow feedbacks) and present day warming (extremely rapid increases in atmospheric greenhouse gas concentrations resulting in rapid temperature increases). During ice age transitions the processes were sufficiently slow that the Earth’s temperature likely was near-equilibrium with the forcings (varying insolation, greenhouse gas levels and associated feedbacks). Now atmospheric greenhouse gas levels are rising far more quickly than the Earth’s temperature is able to keep pace with (the inertia from the massive ocean) and so we still have rather a lot of warming “in the pipeline” from current levels of atmospheric CO2, not to mention the amount of warming yet to be unmasked, as a result of man-made aerosolic countering of enhanced greenhouse-induced warming:

(iii) Your data on temperature/CO2 relationships are laughable. Just to choose one jaw-dropping example, there is one single data point in the Vostock core (1999 data set) that shows an anomalous temperature, and from this you conclude that “the average global temperature 400 years ago was significantly higher than now”! One data point from one location does not an “average global temperature” give. The pukka science carefully collects a range of proxy data from multiple sources using many different methodologies, taken from as many places on Earth as possible to assess careful paleoproxy temperature data that is truly globally (or at least hemispherically) averaged. You (having other fish to fry one suspects than assessing the best possible understanding from the available data) base your entire analysis on one data point, from one data set from one location on Earth. Oh dear!

And so on. Happily the individuals and organizations that address these issues maturely and seriously don't fall for that sort of nonsense....

[***] In fairness to Christopher Scotese, his site is quite good. He does need to update his paleotemperature graph though!

Chris:
Your assertion “…talk a lot of nonsense…” may reveal that you simply do not understand how feedback works. The graphs in the Middlebury link are plots of data from NOAA and other credible sources. They speak for themselves and are as correct as the data sources.

Apparently you accept Scotese’s temperatures. The carbon dioxide level at that time is from GEOCARB III as published in the American Journal of Science. The graph at http://www.globalwarmingart.com/wiki/Image:Phanerozoic_Carbon_Dioxide_png shows a lot of illogical scatter in Royer’s compilation but fair agreement between 30Myr filtered Royer, Copse and GEOCARB III. I have found no rational argument as to why the atmospheric carbon dioxide level should dramatically change prior to the temperature dropping into that ice age. The assertion remains that the temperature dropped while the carbon dioxide level was several times higher than now.

The graph of CO2 and average global temperature during the Phanerozoic (all of the time that there have been complex life forms, the last 550 million or so years) at http://mysite.verizon.net/mhieb/WVFossils/Carboniferous_climate.html is as good as any. A lot of imagination is needed to see any correlation there between atmospheric carbon dioxide and average global temperature.

You say “the warming oceans release CO2 into the atmosphere resulting in further warming”. That would be a ramp up in temperature. But then the ramp up changed direction and became a ramp down. And this direction change in temperature trend happened repeatedly during the last and previous glaciations. That could not happen if there was significant net positive feedback.

For those who understand how feedback works, this temperature trend direction change proves that there is no significant net positive feedback. All that is needed to determine if there is net positive feedback is a temperature trace for a long enough time to average out cyclic variation from random noise and other factors. The temperature trace does not even need to be correct in absolute terms just reasonably accurate in relative terms time-wise. Without significant net positive feedback added atmospheric carbon dioxide does not produce significant increase in average global temperature. Even the flawed GCMs give that result. Those who think they “…know about greenhouse gases and their effects…” apparently do not recognize the significance of this observation.

While determination of the magnitude and even the sign of net feedback in climate may be difficult using climatology (Spencer at a link in 41 above and also Monckton at http://www.aps.org/units/fps/newsletters/200807/monckton.cfm have done it), it is trivial, as described above, for someone who understands feedback, to deduce from the temperature record that net positive feedback does not exist. Many climatologists apparently don't know how feedback works so they don't realize this. Unaware of their ignorance, they impose significant net positive feedback in their GCMs which causes them to predict substantial warming from carbon dioxide increase. Without significant net positive feedback, the GCMs do not predict significant Global Warming. From Monckton’s paper “The IPCC overstates temperature feedbacks to such an extent that the sum of the high-end values that it has now, for the first time, quantified would cross the instability threshold in the Bode feedback equation and induce a runaway greenhouse effect that has not occurred even in geological times despite CO2 concentrations almost 20 times today’s, and temperatures up to 7 ºC higher than today’s.”
Do you realize how many times you said in 46 that the sun started it? These were extracted from your text: “…insolation changes…”, “…primary inducer of the warming is increased solar radiation…”, “…decreased [s]olar insolation resulted in cooling…”, “…one “lowers the heater” that the Earth cools…” Solar variation is certainly a major part of it. Of the list of other possible contributors to climate change, some ignored, some subjectively parameterized; solar wind, clouds, vertical convection, cosmic rays, Milankovitch cycles, etc. and factors not yet discovered, only significant net positive feedback is readily ruled out. Influencing any of the others doesn’t look promising. Humanity needs to adapt to climate change. Warming is not a problem. If it gets too hot or wet or dry where you are at, move. There are currently places that lack permanent occupancy because they are too hot, too cold, too wet or too dry. Half of humanity may starve in the coming glaciation, however, because rice does not grow on ice.

The high rate of change of the level of atmospheric carbon dioxide today is not relevant to climate change since the level of atmospheric carbon dioxide has no significant influence on climate. Eventually, excess atmospheric carbon dioxide will dissolve in the ocean which already holds over 50 times as much as the atmosphere. Interestingly, I have read that the rate of increase of carbon dioxide in the atmosphere is about half of what is calculated based on the amount added by humanity.

In your lawyer-like advocacy and nitpicking of the scarcity of paleo data you appear to have completely missed the point of temperature trend reversals ruling out net positive feedback. I suggest that you break out of the box that you are in, adopt engineer/scientist-like objectivity and learn about feedback.

There are legitimate reasons to constrain the use of fossil fuels. As the level of atmospheric carbon dioxide continues to increase, and it will, humans may find enclosed places becoming ‘stuffy’ sooner than previously. The consumer price rise of liquid fuels as a result of ‘peak oil’ will curtail their use and stimulate alternate fuels such as algae produced biodiesel. I have been antagonistic to coal for decades and am suspicious of claims that mercury, soot and acid can be effectively removed from the exhaust. When humanity gets past their unjustified paranoia regarding nuclear power and start building breeder reactors they will have all of the energy needed for millions of years. Enough to recharge their hybrids and even synthesize liquid fuel to go beyond battery range.

No Scotese's temperatures are horribly incorrect (that's obvious surely). It's not clear where they came from (can you enlighten us?), and they clearly bear little relation to reality or to the paleotemperature data that is compiled extensively in the recent scientific literature (see citations at bottom of post for example).

Try using Google Scholar or visit .edu sites (or your local University library - there are a number of relevant papers at the bottom of this post). In addressing scientific issues, one should address the science.

["The graph of CO2 and average global temperature during the Phanerozoic (all of the time that there have been complex life forms, the last 550 million or so years) at http://mysite.verizon.net/mhieb/WVFossils/Carboniferous_climate.html is as good as any."]

No it isn't. Sadly it's a laughable parody of the data that has been complied in a large number of studies, and it's surprising that someone with an apparent interest in this subject would consider it to be so in the light of the abundant scientific data on this subject (see citations at bottom of this post). Obviously if one puts together a completely false representation of the scientific data on paleoCO2 and paleotemperature one shouldn't be surprised if one is led to fallacious interpretations.

And suggesting that pointing out gross misrepresentation of the science based on ludicrously inadequate graphs using unspecified data on dubious websites with contrived misinterpretation, is "Lawyerlike advocacy and nit-picking", is a delightful lu-lu!

As for feedbacks, I suspect you've managed to be misinformed through poor analysis or the perusal of dodgy sources (Christopher Monckton? isn't this supposed to be about science?). There's no question that raising atmospheric CO2 levels results in a re-equilbration of the Earth's temperature such that internal variations fluctuate around a higher equilibrium temperature (assuming volcanic/solar contributions are flattish), and that this involves feedbacks (e.g. a warmer atmosphere caused by enhanced atmospheric CO2 results in a higher concentration of water vapour.....enhanced warming results in enhanced ice melt and reduced albedo and so on)... The science indicates that the Earth responds to raised CO2 with a raised equilibrium surface temperature near 3 oC (+/- a bit).

I'm not sure why you have a problem with this and feedbacks in general. Clearly during ice age cycles the dominant driver is cyclic variations in insolation due to slow variations in the Earth's orbital properties. It only requires that the insolation cycles dominate over the effects of CO2 (feedbacks included) to observe the relationships between temperature and CO2 levels in the Vostock core that you are so exercised over. If CO2 levels rise from 180-280 ppm over thousands of years(due to very slow solar induced warming) resulting in enhanced direct CO2 (greenhouse) warming with fast positive water vapour feedbacks and slower albedo feedbacks, and then the solar contribution diminishes, much of the atmospheric CO2 will still be there (for hundreds of years) as the temperature cools in the early stages of the next Milankovitch cooling cycle. And as the temperature cools due to decreased insolation, so the water vapour levels drop, even as CO2 levels remain high. That's not difficult to understand at all..

You make some other very odd comments. Yes, high levels of atmospheric CO2 will eventually be drawn out of the atmosphere. This is a very slow process (your own Vostock data show this). And of course "the rate of increase of carbon dioxide in the atmosphere is about half of what is calculated based on the amount added by humanity." Half of the CO2 we've released into the atmosphere has been absorbed by the oceans with a very measurable drop in pH (increased acidity).....already the absorption of our emissions by the oceans is decreasing due to the saturation of the upper oceanic waters. Each of these is problematic.

All in all, you've chosen to use ludicrous data from some website to pursue the unsupported notion that there isn't a relationship between atmospheric CO2 lelvels and the earth's global temperature. And yet the science clearly shows otherwise (e.g. papers cited below). No one disputes the fact that CO2 is a greenhouse gas, and greenhouse gases cause the Earth to warm above its black body temperature (by around 30 oC worth of warming on Earth). Or do you consider that CO2 stops being a greenhouse gas above some concentration or other?

Anyway, here's some of the science that one would hope you might access in place of dodgy websites:

D.L. Royer (2006) "CO2-forced climate thresholds during the Phanerozoic" Geochim. Cosmochim. Acta 70, 5665-5675.
(this is a review compiles much of the published data)

Even more recent studies supplement the information in Royers compilation and cover additional periods with new data sets right through the past several hundreds of millions of years:

The Andean-Saharan issue is simple. The ice age happened and the carbon dioxide level was much higher than now when it started. The chart uses data compiled by Christopher R. Scotese, Ph.D., University of Chicago, 1985, currently an Associate Professor geologist at the University of Texas at Arlington. Research interests include plate tectonics, paleogeography, and paleoclimatology and R. A. Berner, Department of Geology and Geophysics, Yale University. Contrary to your implication, they are university scientists.

My understanding of feedback in a complex system comes from having an advanced degree in Mechanical Engineering and many years of engineering practice including rocketry, nuclear power, and meteorological satellites. Many engineers understand and successfully apply feedback in complex systems and have for many decades. Although climatologists use a somewhat different formulation, the end result is the same.

Your discussion of feedback verifies that you don’t understand feedback very well. That explains why you don’t recognize that the temperature trend reversals during the previous glaciation (not talking about 100,000 year ice age cycles here) prove that significant net positive feedback does not exist in climate.

If you use the same argument regarding the temperature trend reversals as you use for changes from glacial to interglacial then all temperature trends would be reversed by unpredictable solar changes which would make GCMs useless as climate predictors.

I am puzzled as to why you call some of my comments “very odd” and then proceed to agree with them.

The data that you disparagingly refer to as ludicrous is well referenced and came from NOAA as you could have easily discovered.

I say that there is no significant net positive feedback and you claim that I said “there isn't a relationship between atmospheric CO2 lelvels and the earth's global temperature”. Some scientists express their interpretations and you say “science says”. More scientists and engineers are on record declaring that atmospheric carbon dioxide level has no significant influence on climate than there are saying that it does (Not that it matters).

(1) There is unfortuantely no paleoCO2 proxy that coincides in time with the late Ordovician paleoevidence for glaciation. Therefore we don't know the relationship between paleoCO2 and paleotemperature for that particular event. There's no point in pretending otherwise.

(ii) Pretty much every case where we do have contemporaneous paleoCO2 and paleotemperature temperature proxies, the relationship between atmospheric CO2 and temperature is rather clear. See the list of scientific papers in my post #48.

(iii) If one want's to assess scientific issues, one goes to the published science, not to dodgy outdated, and unattributed pictures on websites.

(iv) Christopher Scotese seems a perfectly excellent chap. However his website was last updated around 2002, and his site is principally to illustrate tectonic effects on continental movement. Sadly his site happens to contain a completely incorrect graph of paleotemperature data. It's more of a child-like crude sketch. I've no idea where it comes from...(can you enlighten us?)

(v) I've shown you a long list of papers, including a recent review that compiles all of the data up to around 2005/6. Unfortunately, rather than taking the effort to explore the science on this subject, you prefer to argue over a crude unattributed graph that is clearly incorrect....go figure!

(vi) You have an advanced degree on Mechanical Engineering and so on...and yet you have spent an apparently significant eforrt in putting together a web page full of the most blatant misrepresentations. While real scientists assess multipile paleotemperature data sets obtained with many different methods from as many places on the earth as possible to obtain truly global (or at least hemispheric) paleotemperature estimates, you choose ONE data point, in ONE data set, from ONE place on Earth and presume to aseet that 400 years ago the globally averaged temperature was higher than now...

(vii) Even though that's a dismal piece of misrepresentation, and Scotese's temperature data is clearly incorrect, and your arguments about feedbacks have no basis in science......

..you are still asserting that you are right on these matters whereas all the climate, meterological, ocean, paleoenvironmental scientisits and so on are all incorrect....

I don't think so Dan.....why not make an effort to access the science on these issues. I've given you a wealth of sources that bear exactly on the subjuect of issue that containis the most up to date data.

Graphs of source referenced NOAA data are presented and you see “blatant misrepresentation”.

The proof that significant net positive feedback and therefore AGW does not exist does not use Holocene data but you persist in worrying about a specific data point.

You point out that other scientist’s have different interpretations of the Andean-Saharan ice age and you have decided which ones you agree with. Perhaps you do not realize that A/S is also not a necessary consideration to prove that significant net positive feedback does not exist in climate. The Scotese-Berner assessment of A/S defrays concern for planet-wide runaway temperature rise but the logarithmic decline in infrared radiation intensity with distance from the radiating surface with what is called the ‘saturation’ effect of atmospheric carbon dioxide refutes the ‘tipping point’ nonsense without any other consideration.

Apparently you still don’t understand how feedback works. Perhaps we are not communicating. Let’s try a specific example. Look at the temperature trend from 55,000 ybp to 50,000 ybp. (This is from NOAA Vostok data as graphed in the second graph on the Middlebury website but the EPICA core shows about the same only shifted slightly in time.) See that this uptrend changes to a down trend at 50,000 ybp. This downtrend continues until about 45,000 ybp. This direction change from an up trend to a down trend could not take place if there were significant net positive feedback. Now look at the rest of the graph and see that there are many similar examples.

Only the few who still believe that the rising atmospheric carbon dioxide level will have a significant effect on average global temperature are incorrect.

I am basing my understanding of the strong relationship between paleoCO2 measures and paleotemperature measures right back through the last 500 million years, BASED ON HUNDREDS OF CONTEMPORANEOUS CO2 and TEMP MEASURES (see data in my references cited in the posts above)

You are taking one specific part of the paleodat where there is evidence for glaciation (i.e a coolish/cold Earth) and assuming that there is no relationship with atmospheric CO2. However THERE IS NO CONTEMPORANEOUS PALEO-CO2 MEASURE THAT OVERLAPS THIS PERIOD...and therefore your focus on a specific data point is spurious.

NUMBER 2:

I am basing my understanding of the paleotemperature data of the last 2000 years which indicates that late 20th century and contemporary warming is well above anything experienced during this time period. THIS DATA IS BAED ON NUMEROUS DATA SETS USING NUMEROUS METHODS OBTAINED FROM MANY DIFERENT PLACES ON EARTH.

You are making a blatant misrepresentation of the data by basing your interpretation on ONE data point, from, ONE location, using ONE method.

For some reason you're trying to construct a whole edifice of misrepresentation based on single data points.

And for some reason, despite your assertions of scientific credentials you can't seem to grasp that primary effects (raised CO2 levels) supplemented with feedbacks can be overpowered by other effects (reduced insolation during waning Milankovitch cycles)...